Air filter system, air filter element and method for exchanging an air filter element

ABSTRACT

A filter (1) for filtering air, in particular an air filtering element (30), is provided for releasably fitting into a housing (10) which has a housing upper part (11) and in particular a central tube (20) fastened to the housing upper part (11), and also the housing for the filtering element (30) is provided. The filtering element has a seal (33, 34) for holding the filtering element (1) on the housing upper part (11) and the central tube (20) and for sealing the space (111) between the filtering element (30) and housing upper part (11) when the filtering element (30) is releasably fitted in the housing (10). The seal (33, 34) is connectable in a form-fitting manner to a sealing receptacle (111) of the housing upper part (11) and/or of the central tube (20).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/107,831 filed Dec. 16, 2014, which is a continuation of internationalapplication No. PCT/EP2012/061354 having an international filing date ofJun. 14, 2012 and designating the United States, the internationalapplication claiming a priority date of Jun. 15, 2011, based on priorfiled German patent application No. 10 2011 106 502.8, the entirecontents of the aforesaid international application and the aforesaidGerman patent application being incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a filter element which can be used forfiltering air as well as to a housing for the filter element. Theinvention relates in particular to an air filter element, the housingfor the air filter element and a filter assembly.

Filter elements are used for the filtration of fluid flows or gaseousmedia. They are, for example, used for the filtration of an air flowwhich is directed into a passenger compartment of a motor vehicle. Inthis connection, an air condition installed in the motor vehicle is inparticular used to clean the outside air with regard to harmfulsubstances, odors, etc. contained therein. Appropriate filters or cabinfilters are in this context for example particle filters, odor filtersor a combination thereof.

Furthermore, it is necessary to clean the air, which is directed to aninternal combustion engine, from suspended particles. Such air filters,for example for trucks, construction machines, agricultural machines oreven marine engines have to be designed in a reliable and robust manner,for they can be exposed to extreme mechanical loads during operation.

Normally, filters have a housing with a housing upper part, wherein thehousing can be installed in an exchangeable filter element. Normally,the filter element has a tubular design and is frictionally engaged inthe housing by means of a seal.

BACKGROUND

DE 20 2007 004 475 U1 discloses a filter assembly in which a filterholder features at least one through-hole which serves to sealinglyaccommodate a filter element with an adapter collar.

For example foam made of polyurethanes (PU), also called PU foam, may beused as seal between housing or housing cover and filter element. Suchfoam made of polyurethanes, however, tends to relax after heat storageor due to exposure to high temperatures or temperature change.

In other words, the foam made of polyurethanes is force-free after heatstorage, having lost elasticity. With filter elements frictionallyengaged in the housing this is often the reason why greater criticalmovements between the individual parts occur with vibration excitationof the assembly from the parts housing with housing upper part, seal,and filter element. Such a vibration excitation can, for example, mayoccur during the operation of a motor vehicle into which the filter isinstalled.

SUMMARY

An objective of the present invention is to develop an improved airfilter system, an improved air filter element, and an improved methodfor exchanging an air filter element.

Accordingly, the air filter system serves in particular for the intakeair of internal combustion engines and comprises a housing and at leastone air filter element for filtering air. The housing comprises ahousing upper part with a clean air connection for discharging clean aircleaned in the air filter element from the housing and a sealingreceptacle for a form-fitting connection with a cylindrical, inparticular radially acting seal of the air filter element and forholding the air filter element. The sealing receptacle features acylindrical, from the housing upper part into the interior space of thehousing extending sealing surface which encloses the clean airconnection and to which the seal of the air filter element can beapplied, wherein at the sealing surface an annular projection protrudingradially over the sealing surface is disposed which can be enclosed bythe seal of the air filter element in a form-fitting manner.

The design of the sealing receptacle and of the seal guarantees inparticular that the seal between housing and filter element does notbecome force-free during heat storage.

Advantageously due to the form fit, the filter element is securely heldat the sealing receptacle without axial tension and cannot drop out ofthe receptacle. The seal and/or the housing shape or the sealingreceptacle is, for example, designed in such a way that the form fitfirmly and tightly holds the weight of the filter element loaded withparticles.

The cylindrical shape of the sealing surface can preferably be designedas circular cylinder, elliptic cylinder or oval cylinder. The shapepreferably forms the outer circumference of the air filter element.However, a polygonal, in particular rectangular shape can be chosen.

The air filter element is preferably designed as round filter elementwhich comprises a zigzag folded, closed annular filter bellows thatencloses a central interior space. The filter bellows is sealed on itsaxial ends by end disks, wherein one end disk features a central annularinlet or outlet opening at which a seal for separating raw from cleanside is disposed. However, the air filter element can also feature twozigzag folded, closed annular filter bellows which are arranged oneinside the other and connected with each other in such a way that onefilter bellows can be radially flowed through from the outside to theinside and the other filter bellows can be radially flowed through fromthe inside to the outside. An air filter element with channels extendingin flow direction is also conceivable which are formed by the fact thatone smooth filter media layer and one undulated filter media layer arealternately placed on top of each other and that the channels formedtherebetween are alternately closed.

As filter medium, a flat, porous filter medium can be used in each case,for example individual layers or combinations of cellulose media, glassfiber media, fleeces made of melt-blown or spun synthetic fibers.

In one embodiment, a through-flowable central tube is disposed in thehousing in particular coaxially to and in continuation of the clean airconnection for radially supporting the air filter element, wherein thecentral tube is either detachably installable into the housing or madein one piece with the housing upper part of the housing. Due to thearrangement of the central tube at the housing, a reliable support ofthe filter bellows in operation can be ensured without providing a meansfor support in the exchangeable filter element. This makes it possibleto create a lighter and less expensive design of the filter element.Furthermore, a possibly existing secondary element disposed in thecentral tube is protected by the central tube against mechanical damageswhen the main filter element is installed or removed.

It is advantageous if the central tube is designed in such a way that aseal of the filter element is detachably attachable by interlocking atthe central tube and/or that the central tube is detachably attachableby interlocking at the housing upper part.

In one embodiment, the annular projection protruding radially over thesealing surface is formed by an annular extending central tube collarwhich is firmly connected with the central tube, in particular made inone piece and/or in particular abutting the sealing surface. In thisway, the undercut formed by the projection protruding over the sealingsurface may be easily formed or manufactured. Furthermore, with anunchanged housing, different variations of the air filter element andcentral tube are possible, for example, by varying the length of centraltube, air filter element and housing lower part mountable on the housingupper part different air filter systems with different filter surfacescan be realized with unchanged housing upper part.

In one embodiment, the sealing surface is formed radially outside orinside at a cylindrical collar projecting from the housing upper partinto the interior space of the housing.

In one embodiment, the sealing receptacle is formed by an annular recessor groove in the housing enclosing the clean air connection, inparticular in the housing upper part.

In one embodiment, the sealing surface is formed by a cylindrical,radial inner or outer wall of the recess or groove.

In one embodiment, the central tube is designed in such a way that aseal of the air filter element is detachably attachable to the centraltube by interlocking. This can, for example, be realized by the factthat the seal of the filter element features an undercut in the shape ofa radial annular groove which corresponds to the shape of the projectionof the housing upper part or the central tube. For example, the undercutcan be designed in such a way that the surface of the undercut is spacedapart from the projection when the filter element is installed in thehousing. However, the undercut can, for example, also be designed insuch a way that the surface of the undercut abuts the projection in aforce-free manner or with a slight tensioning when the filter element isinstalled in the housing.

Preferably when installing the seal of the filter element, the seal ispushed over the projection and thereby radially tensioned andelastically deformed, and may form the undercut. Once the sealingsurface of the seal exceeds the projection, it radially abuts thecorresponding sealing surface of the housing. If an undercut is providedin the seal of the filter element, the projection engages into theundercut and thus realizes a form fit in an insertion direction betweenhousing and filter element. However, the form fit can also be realizedwithout the undercut, the projection at the housing permanentlydeforming the seal of the filter element when installed in such a waythat a corresponding undercut is formed in the seal.

The central tube can also be detachably attachable by interlocking tothe housing upper part.

The annular projection can form a closed ring or be interruptedregularly or irregularly.

In one embodiment, this comprises a main filter element and a secondaryfilter element, which is disposed downstream of the main filter elementin flow direction of the air, wherein the main filter element isattachable on the outside of the central tube and the secondary filterelement on the inside of the central tube when the air filter elementsare detachably installed in the housing.

In one embodiment, the main filter element features a seal for holdingthe main filter element at the housing upper part and/or at the centraltube as well as for sealing the space between main element and housingupper part when the main filter element is detachably installed in thehousing, and the secondary filter element features a seal for holdingthe secondary filter element at the housing upper part and/or at thecentral tube as well as for sealing the space between secondary elementand housing upper part when the secondary filter element is detachablyinstalled in the housing. Preferably, both seals and their correspondingsealing surfaces and sealing receptacles feature a configurationaccording to the invention.

Preferably, a radially outwardly facing sealing surface, in particularfor the main filter element, with a radially outwardly facing projectionprotruding over the sealing surface is provided at the housing.

Preferably, a radially inwardly facing sealing surface, in particularfor the secondary filter element, with a radially inwardly facingprojection protruding over the sealing surface is provided at thehousing.

The invention relates furthermore to an air filter element for adetachable installation into a housing of an air filter system inparticular according to the invention, wherein the air filter elementcomprises a seal for holding the air filter element at the housing andfor sealing a space between the air filter element and the housing upperpart when the air filter element is detachably installed in the housing,wherein the seal can be connected with the sealing receptacle of thehousing upper part in a form-fitting manner.

The form fit is preferably realized in radial direction, specificallyone part of the one component, preferably of the housing, engagesradially into the other part, preferably the air filter element. Aform-fitting connection is thereby realized which substantially resistsaxial movement of the filter element out of the seal seat, makingremoval more difficult.

The filter element is preferably an air filter element, for example forfiltering combustion air of an internal combustion engine. However, theinvention can also be used for all liquid filters, for example oilfilters or fuel filters.

The proposed filter element is of easy construction and can bemanufactured at low costs. At the same time; the design of the sealensures that the seal between housing and filter element does not becomeforce-free even with heat storage.

Due to the form fit, the filter element furthermore remains attached tothe sealing receptacle without tensioning and cannot drop out. The sealand/or the housing shape or the sealing receptacle is, for example,designed in such a way that the form fit holds a weight of the filterelement loaded with particles.

In embodiments of the filter element, the same is exclusively insertablyconnectable with a housing or the sealing receptacle. This simplifiesinstallation and/or removal and avoids time-consuming bayonet or screwconnections.

Preferably, the seal is designed in such a way that the filter elementis detachably attachable to the central tube by interlocking. Thus, aparticularly stable and fluid-tight connection can be realized even withoscillations or vibrations of the filter element and/or the housing.

In one embodiment, the seal forms an undercut into which protrudes theannular projection radially when the air filter element is detachablyinstalled in the housing. The undercut may be formed by elasticcompression of the seal by the annular projection.

In one embodiment, the seal is designed in such a way that the filterelement is detachably attachable to the housing upper part and/or to thecentral tube by interlocking, wherein in particular the interlocking ofthe filter element at the housing upper part and/or at the central tubecreates a haptic perception during the detachable installation of thefilter element. The ability to handle the filter element is therebyimproved, for it becomes perceivable whether the filter element has beencorrectly and sealingly mounted.

In one embodiment, the seal of the filter element features an undercutin the shape of a radial annular groove which corresponds in particularto the shape of the projection of the housing upper part or the centraltube. For example, the undercut can be designed in such a way that thesurface of the undercut is spaced apart from the projection when thefilter element is installed in the housing. However, the undercut can,for example, also be designed in such a way that the surface of theundercut abuts the projection in a force-free manner or with a slighttensioning when the filter element is installed in the housing.

The seal is preferably made at least partially of a casting compound,for example of a foamed PUR material. In particular the seal and/or thematerials of the filter element or the housing are designed foroperating temperatures between −30° C. and 90° C. The seal is preferablymade of the same material in one piece with an end disk. Evenfurthermore, the end disk is preferably made of the casting compound andis sealingly connected with the filter bellows during casting.

Furthermore, the seal can feature at least one stiffening element forstiffening the seal.

In one embodiment, the seal has an inside sealing line on the interiorside of the main filter element and a sealing web exterior side.Preferably, the seal has on the sealing web exterior side a plurality ofnotches which are disposed side by side along the circumference of thesealing web.

With the seals according to the invention, the exterior side of thesealing web is meant to generate a contact pressure to the in particularradially inside disposed sealing surface when the filter element isbeing mounted or is mounted in the housing. The exterior side of thesealing web is thereby preferably radially supported at, for example, anannular surface of the sealing receptacle. If such notches are provided,they reduce the pressure or mechanical resistance which is perceivablewhen mounting the filter element.

The invention relates furthermore to a method for exchanging an airfilter element in an air filter system according to the invention inwhich the housing is opened, in particular by loosening a housing lowerpart from the housing upper part, subsequently an air filter element inparticular according to the invention is removed from the housing andfurther subsequently an air filter element in particular according tothe invention is mounted into the housing in such a way that the seal isconnected with the sealing receptacle of the housing upper part in aform-fitting manner.

When installing the seal of the filter element it will preferably firstof all be pushed over the projection and thereby radially tensioned andelastically deformed. Once the sealing surface of the seal has exceededthe projection, it then abuts radially the corresponding sealing surfaceof the housing. If an undercut is provided in the seal of the filterelement, the projection engages into the undercut and thus realizes aform fit in insertion direction between housing and filter element.However, the form fit can also be realized without undercut if theprojection at the housing permanently deforms the seal of the installedfilter element in such a way that a corresponding undercut is formed inthe seal.

With the described filter element, a form fit in the seal with respectto the housing is realized which has the advantage that the seal is keptin position even after aging or after high temperature impact ortemperature change. Therefore, even at high oscillation loads which can,for example, occur during operation of a motor vehicle, criticalmovements between the individual components housing, seal and filterelement are avoided.

The described interlocking of seal and central tube is realized by aspecial design of seal and central tube and generates therefore the formfit in the seal. The advantage of form fit is that the user receives ahaptic feedback when mounting the filter element into the housing whichis generated by snapping in of the form fits.

Another advantage of the described form fit in the seal is that thefilter element cannot drop out of the housing, for example by thegravitational force, even if the housing has been opened for dismountingthe filter element.

Further possible implementations of the invention comprise also notexplicitly mentioned combinations of characteristics describedpreviously or in the following with respect to the examples of anembodiment. In this context, the person of skill in the art will addalso individual aspects as improvements or complements to the respectivebasic form of the invention.

Further embodiments of the invention are subject of the subclaims aswell as of the examples of an embodiment of the invention described inthe following. Furthermore, the invention is explained in detail basedon examples of an embodiment with reference to the attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying Figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the present invention.

Features of the present invention, which are believed to be novel, areset forth in the drawings and more particularly in the appended claims.The invention, together with the further objects and advantages thereof,may be best understood with reference to the following description,taken in conjunction with the accompanying drawings. The drawings show aform of the invention that is presently preferred; however, theinvention is not limited to the precise arrangement shown in thedrawings.

FIG. 1 is a three-dimensional view of an air filter according to one ofthe first examples of an embodiment;

FIG. 2 is a sectional view of the air filter in FIG. 1 into which afilter element is detachably installed according to the first example ofan embodiment;

FIG. 3 is a three-dimensional detailed view of the filter elementaccording to the first example of an embodiment;

FIG. 4 is a detailed view of the filter element according to a secondexample of an embodiment;

FIG. 5 is a detailed view of a filter element according to a thirdexample of an embodiment which is installed in the filter in FIG. 1;

FIG. 6 is a three-dimensional view of a main filter element of thefilter element according to a fourth example of an embodiment;

FIG. 7 is a three-dimensional detailed view of the main filter elementof the filter element in FIG. 6;

FIG. 8 is a detailed view of an air filter system according to a fifthexample of an embodiment; and

FIG. 9 is a detailed view of an air filter system according to a sixthexample of an embodiment.

In the Figures, the same reference numerals denote identical or similarcomponents, unless otherwise stated. Skilled artisans will appreciatethat elements in the figures are illustrated for simplicity and clarityand have not necessarily been drawn to scale. For example, thedimensions of some of the elements in the figures may be exaggeratedrelative to other elements to help to improve understanding ofembodiments of the present invention.

DETAILED DESCRIPTION

In the following, the invention is described by means of a filter forthe combustion air of an internal combustion engine such as, forexample, a motor vehicle. Instead of filtering air, suitable filterelements can be designed, for example, for filtering another gaseous orliquid medium such as, for example, oil.

As shown in FIG. 1, the filter 1 comprises according to the firstexample of an embodiment a housing with a housing upper part 11 which isconnected with a housing lower part 13 via a housing casing 12. Thehousing 10 in FIG. 1 is also a tripartite housing 10. The housing lowerpart 13 is held by means of clamps 14 at the housing casing 12. At thehousing upper part 11 is disposed a raw air connection 15 with which rawair, unfiltered air, can be supplied into the housing 10 in the flowdirection shown by the vertical block arrow. At the housing upper part11 is also disposed a clean air connection 16 with which clean air, aircleaned from impurities, can be discharged from the housing 10 in theflow direction shown by the white block arrow. At the housing casing 12or the housing lower part 13 is disposed a discharge valve 17 with whichparticles, that were contained in the raw air, can be discharged fromthe housing 10. A cyclone filtration is, for example, disposed upstream.The housing 10 has several ribs 18 at the housing upper part 11, thehousing casing 12 and the housing lower part 13 which are, for example,meant to stiffen the housing 10 or the housing upper part 11, thehousing casing 12 or the housing lower part 13. To provide a clearoverview, not all ribs 18 in FIG. 1 are provided with a referencenumeral.

FIG. 2 shows a section through the housing 10 when a filter element 30for filtering air is installed therein. The filter element 30 comprisesa main element 31 and a secondary element 32 which can be mounted in thehousing 10 independent of each other. The main element 31 is meant tofilter first predetermined impurities from the air such as, for example,coarse dust. The secondary element 32 is meant to filter secondpredetermined impurities from the air such as, for example, fine dust.The secondary element 32 is disposed downstream of the main element 31in flow direction of the air, as can be seen by the block arrows in FIG.1 and FIG. 2.

A clamped bracket 19 of a clamp 14 can be recognized in FIG. 2 in orderto connect the housing parts 12, 13 with each other. The housing 10 hasfurthermore a first central tube 20 at which the tubular main element 31of the filter element 30 is disposed. The housing 10 has moreover asecond central tube 21 at which the annular secondary element 32 of thefilter element is disposed. The second central tube 21 has a grid-shapedpipe wall and is fluid-permeable. The first central tube 20 has also agrid-shaped pipe wall and is fluid-permeable, even if this cannot beclearly seen in FIG. 2. The first central tube is attached to thehousing 10, more precisely to its housing upper part 11. This attachmentof the first central tube 20 is realized by interlocking the firstcentral tube 20 to the housing 10, more precisely to its housing upperpart 11. The second central tube 21 can also be attached to the housing10, more precisely to its housing upper part 11. The attachment of thecentral tubes 20, 21 as well as of the filter element 30 is describedlater in detail with regard to FIG. 3 to FIG. 5 which depict each indetail an area in FIG. 2 identified by an arrow A.

FIG. 1 and FIG. 2 show the case in which the housing lower part 13 isattached to the housing casing 12 by means of clamps 14 and brackets 19.To install the filter element 30 or its main element 31 and/or itssecondary element 32, the clamps 14 can be declamped from the housingcasing 12 so that the housing lower part 13 can be removed from thehousing casing 12. In this state, the filter element 30 or its mainelement 31 and/or its secondary element 32 can be pushed along the firstcentral tube 20 and/or the second central tube 21 into the housing 10opened from below. The housing lower part 13 can then be attached againto the housing casing 12 by means of the clamps 14.

FIG. 3 shows the main element 31 disposed on the exterior side of thefirst central tube 20 as well as the secondary element 32 disposed onthe interior side of the first central tube 20 and the second centraltube 21. The main element 31 has an annular seal 33 with anapproximately T-shaped cross section. The seal 33 can also be calledmain element seal 33. The seal 33 can seal the space between mainelement 31 and housing upper part 11. The seal realizes a radial formfit. The material used for the seal 33 is foam made of polyurethanes(PU) or PUR foam. The seal 33 is disposed at one end of the annular mainelement 31. More precisely, the seal 33 is disposed with the crossbeam331 of the T-shaped seal at the end of the annular main element 31. Theline which is vertical with respect to the crossbeam, in other words thefoot 332, of the T projects into a recess 111 of the housing upper part11. The foot 332 of the T forms a projection and can also be calledsealing web 332 of the seal 33. Preferably, the seal 33 is attached tothe main element 31, for example by gluing. The seal 33 has supportsurfaces for radially supporting the main element 31 at the housingupper part 11, wherein this means radial in the direction of the tuberadius of the annular main element 31. Thus, a radial seal is realizedby means of the seal 33. The recess 111 is one part of the space betweenmain element 31 and housing upper part 11 which is to be sealed.

The seal 33 itself may have a recess or undercut 333 into which projectsone part of the first central tube 20, a central tube collar 201, or therecess may be formed into the seal 33 by compression of the seal 33 bythe central tube collar 201 when installed. The central tube collar 201is a projection of the central tube 20. The undercut 333 is disposed inFIG. 3 at the transition from foot 332 to crossbeam 331 of the seal 33.The undercut 333 of the seal 33 is adapted to the shape of one end ofthe central tube collar 201 facing away from the first central tube 20.The undercut 333 and the central tube collar 201 realize, therefore, aform fit. Moreover, the recess 111 of the housing upper part 11 isdisposed in such a way that the end of the central tube collar 201facing away from the first central tube 20 engages into the undercut 333of the seal 33 when the main element 31 of the filter element 30 isinstalled in the housing 10 at the first central tube 20. As a result,the first central tube 20 and the seal 33 engage with each other. To beeven more precise, the central tube collar 201 of the first central tube20 and the undercut 333 of the seal 33 engage with each other. If duringmaintenance of the cabin filter 1 an old filter element 30 is dismountedfrom the housing 10 by loosening the interlocking between the firstcentral tube 20 and undercut 333, a new filter element 30 can then bedetachably installed. The engagement of the central tube collar 201 intothe undercut 333 or its interlocking may be haptically perceived as asnapping sound by the maintenance staff, at least in some embodiments.As a result, the maintenance staff receives a feedback that the mainelement 31 of the filter element 30 is installed in the correct andtherefore safe position in the housing 10.

As can also be seen in FIG. 3, the central tube 20 has moreover at itscentral tube end 202 facing the housing upper part 11 a protrusion 203which projects to the interior side of the first central tube 20 and tothe exterior side of the first central tube 20. The exterior side of thefirst central tube 20 faces the seal 33. The interior side of the firstcentral tube 20 faces the secondary element 32 and the second centraltube 21. On the one hand, the protrusion 203 projects into acorresponding undercut 112 of the housing upper part 11 which exists ina housing upper part web 113 of the housing 10. On the other hand, theprotrusion 203 projects into and may form a corresponding undercut 341of a seal 34 of the secondary element 32. The shape of the protrusion203 is adapted to the desired shape of the undercut 112. Thus, theprotrusion 203 and the undercut 112 can realize a form fit when thefirst central tube 20 is installed in the housing 10, as shown in FIG.3. The shape of the protrusion 203 is also adapted to the shape of theundercut 341. Thus, the protrusion 203 and the undercut 341 can alsorealize a form fit when the first central tube 20 is installed in thehousing 10, as shown in FIG. 3. As a result, the first central tube 20is interlocked with the housing upper part 11 as well as with the seal34 of the secondary element 32. As described above, this interlocking isdetachable.

The seal 34 can seal the space between secondary element 32 and housingupper part 11. The seal 34 can also be called secondary element seal 34.Foam made of polyurethanes (PU) or PUR foam can be used as material forthe seal 34, the same as for seal 33. The seal 34 is disposed at one endof the annular secondary element 31 and abuts a housing upper partprojection 114 which is disposed on the interior side of the clean airconnection 16. The housing upper part projection 114 forms an axial stopfor the seal 34 or the secondary element 32 connected therewith, forexample by gluing. Axial means in the direction of the tube axis of theannular secondary element 32.

FIG. 4 shows a similar detailed view, as in FIG. 3, to explain a secondexample of an embodiment of the filter element 30. The filter 1 and thefilter element 30 of the second example of an embodiment are largelyidentical with the filter 1 and the filter element 30 of the firstexample of an embodiment. Therefore, only the differences between thefirst and the second example of an embodiment are described in thefollowing. For the rest, reference is made to the description of thefirst example of an embodiment.

In contrast to the first example of an embodiment, the filter element ofthe second example of an embodiment has at least one stiffening ring 334in the seal 33. As an example, FIG. 4 shows three stiffening rings 334which are disposed side by side in the seal 33. The ring of thestiffening rings 334 in FIG. 4 is disposed essentially parallel inrelation to the crossbeam 331 of the seal 33. The stiffening rings 334can be made of a harder material than that of the seal 33 such as, forexample, hard plastics or metal.

Thanks to one or more stiffening rings, the seal 33 has a higherstiffness against bending.

FIG. 5 shows a similar detailed view, as in FIG. 3, to explain a thirdexample of an embodiment of the filter element 30. The filter 1 and thefilter element 30 of the third example of an embodiment are largelyidentical with the cabin filter 1 and the filter element 30 of the firstexample of an embodiment. Therefore, only the differences between thefirst and the third example of an embodiment are described in thefollowing. For the rest, reference is made to the description of thefirst example of an embodiment.

In contrast to the first example of an embodiment, the seal 33 of thefilter element 30 of the third example of an embodiment is atwo-component seal. Moreover, the filter element of the third example ofan embodiment has two foot prong projections 335 at the foot 332 or thesealing web 332 of the seal 33 at the side facing the first central tube20 or the secondary element 32. Furthermore, at the foot 332 of the seal33 is realized a duckfoot bend projection 336 on the side facing thefirst central tube 20 or the secondary element 32. The dimensions of thecomplete foot 332 are adapted to the recess 111 of the housing upperpart 11, as shown in FIG. 5. As a result, the foot 332 of the thirdexample of an embedment shown in FIG. 5 can also realize a form fit withthe recess 111 of the housing upper part 11, even if the form fit is inthis case not as distinctive as it is with the form fits of the firstand second examples of an embodiment. The foot 332 can interlock withthe recess 111 of the housing upper part 11 which causes a hapticperception when installing the filter element 30 in the housing 10.

FIG. 6 shows a main element 31 of the filter element 30 according to afourth example of an embodiment in a three-dimensional overall view. Thefilter 1 and the filter element 30 of the fourth example of an embedmentare largely identical with the filter 1 and the filter element 30 of thefirst, second or third example of an embodiment. Therefore, only thedifferences between the fourth and the other examples of an embodimentare described in the following. For the rest, reference is made to thedescription of the first to the third example of an embodiment.

The main element 31 in FIG. 6 is a hollow-cylindrical body whichfeatures at its external circumference several rings 312 which, for thesake of clarity, do not all have a reference numeral in FIG. 6. At thebottom in FIG. 6, the main element 31 is completed by a base ring 313.The seal 33 is disposed at the end of the main element 31 opposing thebase ring 313. The seal 33 has an inside sealing line 337 on theinterior side of the main element 31 and a sealing web exterior side 338of the foot 332 or the sealing web 332. Up to this point, the mainelement 31 is not different from the main element 31 of the first,second or third example of an embodiment.

In this example of an embodiment, however, the seal 33 has in contrastto the first, second or third example of an embodiment a plurality ofnotches 339 which, for the sake of clarity, do not all have a referencenumeral in FIG. 6. The notches 339 are disposed side by side along thecircumference of the sealing web 332. FIG. 7 shows the shape of the seal33 with the notches 339 in enlarged detail.

The sealing exterior side 338 of the seal 33 is meant to generate acontact pressure to the sealing surface when the main element 31 isbeing installed or installed in the housing 10. The notches 339 reducethe pressure or the mechanical resistance which can be perceived duringthe installation of the main element 31. Because of the notches 339, theseal 33 is in fact non-confined or sandwiched in the recess 111 of thehousing upper part. Instead, the sealing web 332 of the seal 33 of themain element 31 can escape into the free spaces formed by the notches339 or fill them by deforming. As a result, a sufficient sealing effectcan, however, be realized by means of the seal 33. However, whenmounting the main element 31, less mounting force has to be applied thanwithout notches 339. The reason for this is that less material is to becompressed radially.

In FIGS. 8 and 9 are shown further examples of an embodiment similar tothe examples of an embodiment according to FIGS. 3 and 4. Theembodiments according to FIGS. 8 and 9 are different from the examplesof an embodiment according to FIGS. 3 and 4 insofar that the firstcentral tube 20 is firmly and undetachably connected with the housingupper part 11. This can, for example, be realized by a one-piece designin plastic injection molding or by a welded joint. A radially inwardlyextending bulge 203 each which protrudes to the interior side of thefirst central tube 20 is disposed at the central tube 20. The interiorside of the first central tube 20 faces the secondary element 32 and thesecond central tube 21. The bulge 203 engages into a correspondingundercut 341 of a seal 34 of the secondary element 32 which is realizedin the shown examples of an embodiment by an elastic deformation of theseal 34. However, the undercut 341 can also be provided as radial groovein the seal 34, as described above.

The seal 34 can seal the space between secondary element 32 and housingupper part 11. The seal 34 can also be called secondary element seal 34.Foam made of polyurethanes (PU) or PUR foam can be used as material forthe seal 34, the same as for seal 33. The seal 34 is disposed at one endof the annular secondary element 32 and abuts a housing upper partprojection 114 which is disposed on the interior side of the clean airconnection 16. The housing upper part projection 114 forms an axial stopfor the seal 34 or the secondary element 32 connected therewith, forexample by gluing. Axial means in the direction of the tube axis of theannular secondary element 32. Radially outside of the central tube 20 isdisposed an annular web 350 with a circular cylindrical sealing surface351 at the housing upper part 11 which features at its end extendinginto the interior space of the housing 10 a radially outwardly extendingbulge 203 which engages into an undercut 333 of the seal 33. FIG. 8shows two variants of the undercut, wherein the cross section of thesmaller undercut corresponds to the cross section of the bulge 203 andthus tightly encloses the surface of the undercut 333 when the mainfilter element 31 is installed. The dashed representation of the variantof the undercut 333 features in inner surface which is spaced from thesurface of the undercut 333 when the main filter element 31 is installedin such a way that a gap is formed between bulge 203 and undercut 333.In the variant shown in FIG. 9, the undercut 333 is formed by an elasticdeformation of the seal 33 (dotted representation).

All examples of an embodiment of the filter 1, the filter element 30 andthe housing 10 described above can be used individually or in allpossible combinations. In this connection, the following characteristicsare conceivable.

Other geometries and dimensions for the filter element 30 as thosedepicted and described can be chosen insofar as the conditions at theinstallation site of the filter element 30 have to be taken into accountand a detachable, haptically perceivable installation of the filterelement 30 in the housing 10 is possible.

Instead of an undercut in the seals 33, 34, the seal 33 and/or the seal34 can also feature a projection or a bulge which engages into anundercut of the housing upper part 11 or of the first central tube 20.However, the variant of the form fit described in the examples of anembodiment between the seals 33, 34 and housing 10 is preferred forstability reasons.

Foil can also be used as material for the seal 33. Likewise, foil canalso be used as material for the seal 34.

The number of notches 339 at the seal 33 can be chosen as appropriate.Only one notch 339 can also be provided. As an alternative, more notches339 than shown in FIG. 6 can also be provided.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in the artappreciates that various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope of thepresent invention. The benefits, advantages, solutions to problems, andany element(s) that may cause any benefit, advantage, or solution tooccur or become more pronounced are not to be construed as a critical,required, or essential features or elements of any or all the claims.The invention is defined solely by the appended claims including anyamendments made during the pendency of this application and allequivalents of those claims as issued.

What is claimed is:
 1. An air filter system comprising: an air filterelement including a filter media; an annular seal having a contact zoneconfigured to form a friction grip to hold the filter element, theannular seal arranged on an axial end of the filter media including: aradially extending cross beam arranged directly on the axial end of thefilter media; an axially outwardly extending elastic sealing web or footformed on an axially outer side of the cross beam and extending axiallyoutwardly away from the axial end of the filter media and cross beam;and a flat cylindrical sealing surface formed on a radially inner orouter side of the axially outwardly extending elastic sealing web orfoot and spaced axially outwardly away from the radially extending crossbeam; wherein the sealing surface of the annular seal is arrangedaxially outwardly away from the radially extending cross beam; a housingincluding a housing upper part; a clean air connection for dischargingclean air from the housing; a sealing receptacle sealably engagingagainst and mounting the radial acting seal of the filter element in aform-fitting tight-fit connection, the sealing receptacle spaced awayfrom the radially extending cross beam of the annular seal, the sealingreceptacle formed on an interior wall of the housing; wherein theform-fitting connection mountably holds the air filter element to thehousing; wherein the housing upper part includes the sealing receptaclehaving a cylindrical extending sealing surface extending from the upperhousing part; wherein the cylindrical extending sealing surface enclosesthe clean air connection; wherein the cylindrical extending sealingsurface receives the sealing surface of the annular seal of the airfilter element; an annular projection arranged in the housing andprotruding radially over the sealing surface of the sealing receptacleand arranged on and at the sealing surface of the sealing receptacle,the annular projection enclosed by the radial acting seal of the airfilter element in a form-fitting manner; wherein the form-fittingtight-fit connection is provided by the radial projection engagingradially against and pressing radially into the contact zone,elastically compressing the annular seal to radially compress annularseal to form a friction grip by forming a radial groove into the annularseal when the filter element is installed in the housing, providing theform-fitting tight-fit connection mountably holding the air filterelement to the housing, wherein the cylindrical extending sealingsurface of the sealing receptacle is spaced axially away from theradially extending groove formed into the annular seal.
 2. The airfilter system according to claim 1, wherein a through-flowable centraltube is disposed in the housing coaxial to and as a continuation of theclean air connection, the through-flowable central tube supporting theair filter element; wherein the central tube is either detachablyinstallable into the housing or made unitary in one piece with thehousing upper part of the housing.
 3. The air filter system according toclaim 1, further comprising an axially extending central tube, thecentral tube having openings for radial flow through a circumferentialwall of the central tube, the central tube having an annular collarextending radially outwardly from the central tube, a radial outer sideof the annular collar forming the annular projection which forms theradial groove into the annular seal when the filter element when thefilter element is in an installed state; wherein the annular projectionis arranged at an axially inner end of a radially inner wall of thesealing receptacle and protrudes radially outwardly over the axiallyinner end of the radially inner wall of the sealing receptacle; whereinthe central tube collar is firmly connected with the central tube, madein one piece of the same material with the central tube or abuttingagainst the sealing surface.
 4. The air filter system according to claim1, wherein the sealing surface is formed radially outside or inside at acylindrical collar projecting from the housing upper part into theinterior space of the housing.
 5. The air filter system according toclaim 1, wherein the sealing receptacle is formed into and by the upperhousing part by an annular recess or groove in the housing radiallysurrounding the clean air connection; wherein the sealing receptacleformed by the housing has a radially outer wall and a radially innerwall defining a “U”-shaped sealing receptacle into which the axiallyoutwardly extending sealing web or foot of the filter element isreceived and radially sealed to the housing.
 6. The air filter systemaccording to claim 5, wherein the sealing surface is formed by theradially inner or radially outer wall of the recess or groove; whereinthe sealing surface of the radially inner or radially outer wall of therecess or groove is cylindrical.
 7. The air filter system according toclaim 1, wherein the central tube is designed in such a way that a sealof the air filter element at the central tube is detachably attached byinterlocking engagement or that the central tube is detachably attachedby interlocking engagement at the housing upper part.
 8. The air filtersystem according to claim 1, wherein the annular projection forms acircumferentially closed ring; or wherein the annular projection is aring that is interrupted regularly or irregularly around its'circumference.
 9. The air filter system according to claim 2, whereinthe air filter element is a main filter element; the air filter systemfurther comprising a secondary filter element, which is disposeddownstream of the main filter element in flow direction of the air;wherein the main filter element is arranged on and attached on theoutside of the central tube; and wherein the secondary filter element isarranged within an interior of the central tube when the main air filterelement and secondary air filter element are detachably installed in thehousing.
 10. The air filter system according to claim 9, wherein themain filter element wherein the annular seal securely holds the mainfilter element onto the housing upper part or at the central tube;wherein the annular seal seals a space arranged between the main elementand housing upper part when the main filter element is detachablyinstalled in the housing; and the secondary filter element includes aseal for securely holding the secondary filter element onto the housingupper part or at the central tube; wherein the secondary filter elementseal seals a space arranged between the secondary element and thehousing upper part when the secondary filter element is detachablyinstalled in the housing.
 11. A filter housing for receiving an airfilter element, the filter housing comprising: a housing upper part; aclean air connection for discharging clean air from the housing; anannular sealing receptacle formed as an annular U-shaped groove formedinto an interior wall of the filter housing, the annular groove openingin an axial direction, wherein the annular sealing receptacle includes acylindrical extending sealing surface extending axially from the upperhousing part; wherein the cylindrical extending sealing surfacesurrounds and encloses the clean air connection; wherein the cylindricalextending sealing surface is configured to receive an annular seal ofthe air filter element; a central tube is disposed in the filter housingas a continuation of the clean air connection, the central tube of thefilter housing sized for being received into the air filter elementduring installation of the air filter element into the filter housingand to support the air filter element relative to the filter housing;wherein the central tube is detachably installed into the filter housingor made unitary in one piece with the filter housing; wherein thecentral tube has an annular collar extending radially outwardly from aradially outer side of the central tube, a radial outer side of theannular collar forming an annular projection which protrudes radiallyover the cylindrical extending sealing surface of the U-shaped grooveformed into the interior wall of the filter housing; the annularprojection and annular sealing receptacle configured to form aform-fitting tight-fit connection with the annular seal of the airfilter element during installation of the air filter element in thefilter housing, by radially compressing an annular region of the annularseal to form a annular groove into which the annular projection isreceived.
 12. The filter housing according to claim 11, wherein theannular projection forms a circumferentially closed ring; or wherein theannular projection is a ring that is interrupted regularly orirregularly around its' circumference.